can you be a little more specific with how you checked J6_RF? You know that the center gold dot is supposed to have continuity with the pad closest to the filter right? Are you saying that the gold dot also has continuity with the other pads?

You have to be more specific---exactly what two parts of the socket are you testing for continuity? If it is center gold pin and the pad leading to the filter then that IS supposed to beep. If it is the circular edge of the socket to the three other pads then that IS supposed to beep. If it is the center gold pin to the circular edge then that is NOT supposed to beep.

It might help you to compare to a known good phone. I doubt you have an antenna problem at all.

1 Answer

I'm not sure what you mean by "burnt" do you see black marks/visible damage, water damage oxidation?

If no---then in my experience no WiFi in a 4S is always the WiFi chip itself needs to be replaced.

If yes---then in my experience it is the WiFi coil that is short due to water damage.

I, too, used to take off this filter and I know there are several solutions out there that recommend taking of the filter to restore WiFi---this is generally helpful only because the heat of that operation will sometimes "reflow" the WiFi chip. Of course it is not an actual reflow, but that chip does like to get warmed up if it is acting up.

If you've tried 'reflowing' the chip, then you'll have to have it replaced to get your WiFi back.

Actually my problem is black screen and vibrating while in charging.even I restored my phone successfully but no display backlight.you know apple designed for some safety for logic board to prevent more damage by any power problems and parts damage or short and if any connector not properly adjust.In the case when I phone get some hardware issues itself stop the some functions by auto power cut and this the black screen is part of this operation.Actually iphone alert us that something wrong with your hardware.

Oh heavens Jay, you are barking up the wrong tree! Your troubleshooting for a no backlight problem looks like this:

1.) Try a new display.

2.) Confirm that you have power (which you've done by connecting to iTunes)

3.) Find the visible board damage----almost always it will be the backlight filters near the LCD connector, or the LCD connector itself. Repair this area.

4.) If still not solved, consider backlight coil or diode

5.) If still not solved and you've confirmed the entire backlight circuit is functional (extremely rare--I've only seen this once in hundreds of phones) consider that the phone may have a chip level defect that is preventing the phone from exiting DFU mode which does have a black screen.

(cont) There is no "you know Apple designed for some logic board safety to turn off the backlight because of some short" Nah. That's kooky talk.

The way a short works is that current is able to find a 'short' path and doesn't have to travel through all the resistance of the circuitry of the phone---that's why the screen doesn't power on if there is a full short. Also, the PHONE doesn't power on---you won't be able to have the phone powered on and able to communicate with iTunes if you have a short in the phone like you are trying to troubleshoot.

my display is black,vibrating while charge.As I told you in this bad situation I restored my phone successfully by itunes.I checked my other phone's working display with this phone but same black no backlught.How can I find any short?

Like I said earlier: "3.) Find the visible board damage----almost always it will be the backlight filters near the LCD connector, or the LCD connector itself. Repair this area. "

FL4 is one of the backlight filters. If it is missing, display will never work. This is your problem. You need to replace it, or repair the line there. All this business of shorts, antennas, and these other components you are listing are totally not relevant to this problem.

if you are good at microsoldering, then the solution is straightforward--you'll need to tie a thin wire into the remaining nub of the trace that was under the pad and then connect it to the opposite pad of FL4. This is a robust repair. I don't recommend a solution attempting to run a wire almost the entire length of the phone to tap into the backlight diode---the diode component completely covers the pad and it would be very difficult to make a connection there without destroying the diode with heat, and it would be a weak solution to have such a long jumper wire in the phone that is carrying the high LCD voltage---just not a good idea when a simple solution exists. If you're not confident that you can connect what is left of the trace at the FL4 then you might be at the point where it makes sense to send this one out for repair.

I think you only needed to replace FL4. I would think that if it doesn't work you should use a multimeter to find out what is the problem. Do you have continuity from the backlight diode to the LCD connector? Are you sure you've placed the diode in the right orientation. Are you seeing voltage out of the diode etc.

It doesn't make sense to keep replacing components on this phone--each time you do that you are introducing another variable and complicating the problem.

You actions make absolutely no sense to me. You have a backlight problem, WHY are you removing U18_RF which is part of the baseband?????? And L19_RF which is part of the GPS???????

Leave Q3 and U6 alone.

You can't bypass the backlight diode, D1, it is required. You need to replace all the components that you have removed, and once done your solution is very simple---the problem is FL4. Only FL4. Replace FL4. No other components are involved. The backlight circuit requires contintuity between D1 and the LCD connector. You must replace FL4.

If you have done that, then check continuity between the diode and the LCD connector. If there is no continuity, then your FL4 replacement didn't work. If there is and still no backlight, then the problem is that the diode is burned.

Forget about all these unrelated components. Backlight problems are very straightforward.

You realize that L18 and L18_RF are two different components, and that L19 and L19_RF are two different components, right? Yes, L18 and L19 are of course both required. As is the backlight diode D1 which, like all diodes, is very sensitive and easily damaged. It is also required to be placed in only one direction, it can't be flipped around. You never mentioned that you had manipulated L18 and L19, but if you have then yes, you need to put them back---they are required for backlight function.

oh sorry,I talking about L18_RF and L19_Rf .I removed both and created jumper for L18_RF(also tried without jumper) but bad luck,L19_RF still missing.I removed diode(D1) and bridged to fl4.actually L19_RF pcb line damaged when I was removing it but ok I will tell you when I set this three components properly.Now I finding L19_RF contacts!

that just means that you have charge in your battery and it is going into the phone. it is normal and doesn't have anything to do with display. i don't understand how you choose these random components to focus on. post again after you've replaced the backlight coil L19, diode D1 and checked FL4 to make sure that it has continuity from the LCD connector through FL4 to the backlight diode. you will never solve your display problem if you keep getting sidetracked by components that are not relevant for display.

Oh sorry my master guide,you are absolutely right that I am choosing random components for solve my problem and this is not correct way!

But I am little confused: I think these components are connected and passing voltage to Fl4.

Let me explain:I observed and start from-

1)C603_RF >L18_RF>D1 diode>C134_RF>>>FL4

C603_RF passing voltage to FL4 via these components.

As I told you that my FL4 pcb layer broke(damaged) so I cant resolder it so I wired bridge with C21_RF(connected with FL4) and other side with C134_RF.But still no backlight and checked voltage for this bridge,multimeter showing -(minus)3.80 volts.

I created bridged bypassed L18_RF and D1 diode(I have no extra components now but I am finding in market) so till then I tried with this strategy..but bad luck!

One more shocking thing that L19_RF and C182_RF missing and pcb layer also broked.

Jay, I've been following this thread from the beginning. I noticed one important thing. you are all over the map. You do not take directions well and replace parts at random. STOP. I am amazed by jessabethany and her patience. STOP replacing parts at random and STOP confusing the issue. By now you do not even know anymore what the issue is. I suggest that you STOP everything that you are doing. Follow the advice that is given to you and STOP adding to it.

@Jay, nobody says to kill your horse. But if your horse is badly injured, why do you try to injure it more? If your horse broke its hind leg why are you trying to fix its ears? Focus on what the issue is and listen to what the doctor tells you on how to fix your horse.

I dont know actual value for both parts,but I have to specify location:L18_Rf (found backside of pcb) and L18 (found front side of pcb) correct?

I replaced two parts: L18(front side near D1),D1(diode). ok tell me what now? I am taking you very seriously for every step ,word,component and action so please trust me I never ignored you,now I want your next step!

it is always the same. replace FL4. If FL4 has damaged pads, then you need to make a microjumper to connect the tiny nub of the trace that is left from where the pad is torn to the other pad. You must have continuity across FL4. In addition, you need to have L18 and D1 in original condition. Take a look at a picture of a recent repair that I did to restore a backlight in another phone--this is not FL4 in the 4S, but it is a similar situation. The pads were gone, and a microjumper was required to restore continuity in the backlight line. https://www.facebook.com/mendonipadrehab...

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